LITHOSPHERIC CONTROLS ON INTRACONTINENTAL MOUNTAIN BUILDING AND EARTHQUAKE HAZARDS IN THE GOBI CORRIDOR REGION OF CENTRAL ASIA, AND COMPARISONS WITH THE INTERIOR OF NORTH AMERICA

The huge deformation field north of Tibet is arguably Earth’s best region for studying lithospheric controls on continental interior reactivation and intraplate earthquake hazards. Actively forming mountain ranges such as the Gobi Altai, Altai and Tien Shan occur in various stages of structural development and most of the region has low precipitation rates enabling the tectonic signal to be clearly expressed in the landscape. The distribution of reactivated crust is strongly influenced by the location of cratonic blocks (e.g., Tarim, Baidrag, Siberian). Cratonic margins are particularly susceptible to reactivation because they are rheological boundaries between cold stiff Precambrian crust and mechanically and thermally weaker Phanerozoic terrane collages. Central Asia differs fundamentally from the interior of North America because it contains the vast Altaids terrane collage in the heart of the continent (rheologically ‘soft core’), whereas North America contains Proterozoic basement in its interior (‘hard core’) with younger terrane collages along the perimeter of the continent.

The region between Northern Tibet and the Hangay Dome in Mongolia localizes Late Cenozoic intraplate reactivation in response to compressional stresses derived from the Indo-Eurasia collision 2000+kms to the south due to: 1) diffuse Jurassic-Cretaceous Basin-and Range style crustal extension that thinned the crust and compartmentalized it into rift basins with variable thicknesses of sedimentary infill that likely generated variations in Moho temperatures; 2) thermal weakening of the crust due to widespread Pz-Mz granitization and Jurassic-Miocene basaltic volcanism; 3) pre-existing sutures, faults, metamorphic fabrics and sedimentary strike belts favorably oriented for reactivation; and 4) the presence of rigid Archean basement beneath the Hangay region of Mongolia that serves as a ‘passive indentor’ focusing crustal reactivation around its southern and western margins. The kinematics of Quaternary faulting in the region is fundamentally controlled by the angular relationship between SH_max and pre-existing structural trends. Historical seismicity indicates that tectonic loading is shared by a diffuse network of potentially active faults challenging standard earthquake hazard models.